fix(sdk): reconnect protocol SSE after clean EOF

[Daniel Peng (original4422)]

Summary

• treat clean SSE EOF as an unexpected disconnect while the event-stream handle remains active
• route it through the existing reconnect callback, retry budget, and backoff path
• preserve terminal behavior for explicit handle or transport close
• add focused coverage for event delivery across reconnect, zero retry budget, and explicit close

Root cause

ProtocolSseTransportAdapter.openEventStream() only reached its reconnect logic when stream consumption threw. A successful SSE response that ended normally closed the shared queue and returned, leaving the retained thread stream handle unable to observe later events.

The fix keeps explicit abort/shutdown terminal, but turns an otherwise clean EOF into the same existing unexpected-disconnect path. It does not introduce a second retry loop or change replay cursor behavior. PR #2689 modifies adjacent durable cursor handling and should compose with this narrow EOF-boundary change.

Test plan

• pnpm exec vitest run src/client/stream/transport/http.test.ts --reporter=verbose (from libs/sdk): 20 passed, no type errors
• pnpm --filter @langchain/langgraph-sdk test: 53 files / 778 tests passed, no type errors
• pnpm format:check: passed (440 files)
• pnpm lint: passed (1,162 files, 0 warnings/errors)
• pnpm --filter @langchain/langgraph-sdk build: passed, including attw and publint
• pnpm build: 25/25 tasks passed

Fixes #2701

[changeset-bot]

🦋 Changeset detected

Latest commit: f74e3d2

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 5 packages

Name	Type
@langchain/langgraph-sdk	Patch
@langchain/angular	Patch
@langchain/react	Patch
@langchain/svelte	Patch
@langchain/vue	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[Copilot]

Pull request overview

This PR fixes a LangGraphJS SDK transport bug where a thread-centric SSE subscription handle could remain “active” while the underlying SSE response ended cleanly, preventing subsequent events from being delivered and bypassing the existing reconnect/backoff logic.

Changes:

• Treats clean SSE EOF as an unexpected disconnect (unless explicitly aborted/closed) so it flows through the existing reconnect path.
• Adds targeted transport-level tests covering clean-EOF reconnect, zero retry budget behavior, and explicit close behavior.
• Publishes a patch changeset describing the reconnect-after-EOF fix.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
libs/sdk/src/client/stream/transport/http.ts	Routes clean SSE EOF through the reconnect/error path rather than silently closing the shared queue.
libs/sdk/src/client/stream/transport/http.test.ts	Adds focused tests for clean-EOF reconnect behavior, retry-budget exhaustion, and explicit close behavior.
.changeset/steady-streams-reconnect.md	Declares a patch release note for reconnecting SSE streams after clean EOF.

---

💡 Add a code-review agent skill or configure MCP servers for context-aware, tailored reviews. Learn more in the docs.

[pkg-pr-new]

Open in StackBlitz

@langchain/langgraph-checkpoint

npm i https://pkg.pr.new/langchain-ai/langgraphjs/@langchain/langgraph-checkpoint@2708

@langchain/langgraph-checkpoint-mongodb

npm i https://pkg.pr.new/langchain-ai/langgraphjs/@langchain/langgraph-checkpoint-mongodb@2708

@langchain/langgraph-checkpoint-postgres

npm i https://pkg.pr.new/langchain-ai/langgraphjs/@langchain/langgraph-checkpoint-postgres@2708

@langchain/langgraph-checkpoint-redis

npm i https://pkg.pr.new/langchain-ai/langgraphjs/@langchain/langgraph-checkpoint-redis@2708

@langchain/langgraph-checkpoint-sqlite

npm i https://pkg.pr.new/langchain-ai/langgraphjs/@langchain/langgraph-checkpoint-sqlite@2708

@langchain/langgraph-checkpoint-validation

npm i https://pkg.pr.new/langchain-ai/langgraphjs/@langchain/langgraph-checkpoint-validation@2708

create-langgraph

npm i https://pkg.pr.new/langchain-ai/langgraphjs/create-langgraph@2708

@langchain/langgraph-api

npm i https://pkg.pr.new/langchain-ai/langgraphjs/@langchain/langgraph-api@2708

@langchain/langgraph-cli

npm i https://pkg.pr.new/langchain-ai/langgraphjs/@langchain/langgraph-cli@2708

@langchain/langgraph

npm i https://pkg.pr.new/langchain-ai/langgraphjs/@langchain/langgraph@2708

@langchain/langgraph-cua

npm i https://pkg.pr.new/langchain-ai/langgraphjs/@langchain/langgraph-cua@2708

@langchain/langgraph-supervisor

npm i https://pkg.pr.new/langchain-ai/langgraphjs/@langchain/langgraph-supervisor@2708

@langchain/langgraph-swarm

npm i https://pkg.pr.new/langchain-ai/langgraphjs/@langchain/langgraph-swarm@2708

@langchain/langgraph-ui

npm i https://pkg.pr.new/langchain-ai/langgraphjs/@langchain/langgraph-ui@2708

@langchain/langgraph-sdk

npm i https://pkg.pr.new/langchain-ai/langgraphjs/@langchain/langgraph-sdk@2708

@langchain/angular

npm i https://pkg.pr.new/langchain-ai/langgraphjs/@langchain/angular@2708

@langchain/react

npm i https://pkg.pr.new/langchain-ai/langgraphjs/@langchain/react@2708

@langchain/svelte

npm i https://pkg.pr.new/langchain-ai/langgraphjs/@langchain/svelte@2708

@langchain/vue

npm i https://pkg.pr.new/langchain-ai/langgraphjs/@langchain/vue@2708

commit: f74e3d2